Soil Amplification Factor of Seismic Ground Motions in Laho (PMO), Kumang (SKO) and Sumandak (SBO) in Malaysian Offshore

• Main Author: Lee, Yik Hoe
• Format: Final Year Project
• Language: English
• Published: IRC 2015
• Subjects: TA Engineering (General). Civil engineering (General)
• Online Access: http://utpedia.utp.edu.my/14624/1/DISSERTATION-%20LEE%20YIK%20HOE%2013851.pdf; http://utpedia.utp.edu.my/14624/

Distant earthquakes in Sumatra and Sulawesi might possess hazard to the offshore platforms in Malaysia underlain by soft soils as the soils might amplify the seismic waves that reach the bedrock of Malaysia. A study of the soil amplification factors in PMO, SKO and SBO is necessary to reduce the downtime loses and onsite casualties of the offshore platforms. This research is one of the pioneers for Malaysian offshores. Thus, Laho in PMO, Kumang in SKO and Sumandak in SBO are selected as three representative case studies for this research. The shear wave velocities of the soils at the selected sites are estimated using published cone penetration test correlation equation. The input motion is based on the strongest earthquake recorded in MMD station near to the selected sites between year 2004 and 2007. A second analysis is conducted by scaling the earthquake recorded to 0.06g to simulate the shaking caused by an earthquake with a return period of 475 years in Malaysia. Onedimensional equivalent linear site response analysis is selected and performed by DEEPSOIL v5.1. The unscaled earthquakes (PGA= 0.0015g) generate high amplification factors but they are associated with very low levels of earthquake shaking which hardly harm the structure on site. The scaled earthquakes (0.06g) generate relatively lower amplification factors which are caused by the nonlinear behaviour of soils. The scaled earthquake also generates a peak spectral amplification at a longer period. However, the lower amplification factors of 1.6 (period 0.4s-2.0s) and 3.5 (period 3.5s) in Sumandak should be taken into account in the design of structure because they are associated with PGA of 0.06g which is significant enough to damage the platforms on site, especially if the seismic waves are amplified and the structure has a natural period close to the amplified periods. This research also shows that the impedance contrast of shear wave velocities at the boundary of two soil layers amplifies the seismic waves. Besides, the soil amplification factors depend on the intensity of shaking